core/vm: fast push/pop/swap/dup

[holiman]

WIP.

This PR breaks consensus theoretically, because if there's a push outside the range of the code, we just push a zero on the stack. In practice, that's fine, because execution will stop at that point anyway.

There's something odd happening. I'm not getting any test failures, but

[user@work go-ethereum]$ ./build/bin/evm  --bench --codefile snailtracer.hex run  1>/dev/null
EVM gas used:    2645349802
execution time:  803.879902ms
allocations:     1073482
allocated bytes: 178875253

The gas used is funky. I think it may be because the bench flag makes the execution reuse the same state, and does not reset it between runs. So if the bench is invoked several times, it can report different values.

Some synthetic benchmarks:

name           old time/op    new time/op    delta
SimpleLoop-6      157ms ± 2%     157ms ± 1%     ~     (p=0.436 n=9+9)
PushPopLoop-6     144ms ± 1%      75ms ± 2%  -47.70%  (p=0.000 n=9+10)
SwapDupLoop-6    57.0ms ± 1%    61.6ms ± 4%   +8.03%  (p=0.000 n=8+9)

name           old alloc/op   new alloc/op   delta
PushPopLoop-6    50.4kB ± 0%    50.1kB ± 0%   -0.59%  (p=0.000 n=10+8)
SwapDupLoop-6    52.1kB ± 0%    52.1kB ± 0%     ~     (p=0.066 n=10+10)

name           old allocs/op  new allocs/op  delta
PushPopLoop-6      74.7 ± 1%      72.0 ± 0%   -3.61%  (p=0.000 n=10+10)
SwapDupLoop-6      72.7 ± 1%      73.0 ± 0%     ~     (p=0.294 n=10+8)

[holiman]

Master:

[user@work go-ethereum]$ ./build/bin/evm-master -statdump --codefile snailtracer.hex run  1>/dev/null
EVM gas used:    305382972
execution time:  369.50483ms
allocations:     398320
allocated bytes: 71044280

This PR:

[user@work go-ethereum]$ ./build/bin/evm -statdump --codefile snailtracer.hex run  1>/dev/null
EVM gas used:    305382972
execution time:  327.825754ms
allocations:     398310
allocated bytes: 71040024

[holiman]

Update with go1.14.4. I ran them three times each, took the best time

[user@work go-ethereum]$  ./build/bin/evm-master -statdump --codefile snailtracer.hex run  1>/dev/null
EVM gas used:    305382972
execution time:  374.332693ms
allocations:     2353
allocated bytes: 57102856

[user@work go-ethereum]$  ./build/bin/evm-21193 -statdump --codefile snailtracer.hex run  1>/dev/null
EVM gas used:    305382972
execution time:  316.023492ms
allocations:     2330
allocated bytes: 57097896

[holiman]

Thiis now on benchmarker: https://geth-bench.ethdevops.io/d/Jpk-Be5Wk/dual-geth?orgId=1&var-exp=bench03&var-master=bench04&var-percentile=50&from=1591781494201&to=now&refresh=5s

bench03 is this PR, bench04 is master.